Grid controlled electron tube



Jan. 25, 1949.

P. W. CHARTON .GRID CONTROLLED ELECTRON TUBE 2 Sheets-Sheet 1 Filed Nov. 25, 1945 Jan. 25, 1949. P. w. CHARTON GRID CONTROLLED ELECTRON TUBE Filed Nov. 23, 1945 2 Sheets-Sheet 2 TEL T =l.lE.

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Patented Jan. 25, i949 GRID CONTROLLED ELECTRON TUBE Paul W. Charton, Montclalr, N. J., assignor, by to Philco Corporation, Philadelphia, Pa., aborimratlon of Pennsylmesne assignments,

Vania Application November 23, 1945, Serial No. 630,320

' A principal object of the inventionis to provide J a grid-controlled electron tube having a novel 18 Claims. 01. 250-27.5)

grid construction and arrangement for improving certain operating characteristics of the tube.

Another object is to provide a grid-controlled electron tube with improved plate current cutoff characteristics.

Another object is to provide a multi-grid arrangement having uniformity of potential along the effective control area of one of the control rids.

A'feature of the invention relates to a multigrid electron tube having a series of grids which are seriall traversed by the emitted electrons, at least one of the grids having a special configuration and orientation with respect to the cathode so as to reduce the disturbing eflects of electronic back-coupling between the grids.

In the great majority of grid-controlled electron tubes, because of the asymmetry of the various electrodes, the plate current cutoff is far from uniform and causes an objectionable trailing plate current-grid voltage characteristic. This is particularly true of those tubes with oval or elliptical grids, or flat grids with round plates, or fiat grids with a round cathode, and the like.

Another feature relates to an electron tube having a novel grid. construction such that the electrons from a suitably located -cathode appreach the grid wires at a substantially uniform angle. As a result, it is possible to design a tube so that it possesses substantially uniform plate current cutoff characteristic along the effective length of the grid wires.

"A further feature relates to an electron tube having a cathode, an anode, and an auxiliary collector electrode, as well as a grid located between the cathode and anode and having its effective control area in the configuration of an arc of a logarithmic spiral whereby a substantial number of electrons which are reflected or repelled from the grid'wires follow trajectories directed towards said auxiliary collector.

A further feature relates to the novel organization, arrangement and relative location of parts which cooperate to provide an improved frequency converter tube of the multi-gridtype.

Other features and advantages not specifically enumerated will be apparent aftera consideration of the following detailed descriptions and the appended claims. 1

In the drawing which represents certain typical embodiments,

Fig. -1 is a diagrammatic plan view of a tube embodying the electrode arrangement'according to the invention.

Figs, 2, 3, 4 and 5 are respective modifications ofFig, 1.

Fig. 6 is a composite schematic-wiring diagram showing one manner of using tubes of Figs. 1 to 5.

Fig. 7 is a composite schematic wiring diagram of a further modification of the invention.

Fig. 8 18a diagrammatic plan View of a still further modification.

Fig. 9 is a plan view of a modification of the rid structure according to the invention.

Fig. 10 is a front elevation of Fig. 9.

Fig. 11 represents a still further modification of the grid structure according to the invention.

Fig. 12 is a front elevation ofFig, 11.

While the inventive concept is capableof em bodiment in a wide variety of tubes, it is particularly useful in so-called frequency converter or mixer tubes such as those of the electronically coupled oscillator type. It will be understood however, that the invention can be embodied in any tube construction where the problem of reflected or repelled electrons is present, which electrons if not suitably directed, will interfere with the desired operational characteristics of the tube. The invention is also useful in any tube where a substantially uniform plate current cutoff characteristic for a signal excitedcontrol grid is required. It will be understood therefore, in illustrating the invention in a frequency converter or mixer tube that this is done merely for purposes of explanation and not by way of limita tion.

Referring to Fig. 1, there is shown in diagrammatic plan view a tube embodying certain features of the invention, and wherein the numeral l'represents any suitable evacuated enclosing bulb or envelope within which the various electrodes are suitably mounted and held in proper spaced relation by any of the expedients well known in the electron tube art. For simplicity of'explan-atiomeach of the grid electrodes is shown schematically in the drawing by a dotted line which, however, is intended to represent any well-known fo'raminous grid structure comprising for example, one or more parallel side rods or uprights for each grid, and between which ex tend the so-calledspaced laterals or grid wires. rue nds'may be formed by helically winding the fine wire laterals around a pair of side rods to which-the helical turns are suitably fastened.

and-provided internally with an insulated heater It will be understood however, .that cathqde 2 may be in the form of a substantially straight coated filament.

successively surrounding lthej .zcathode- ,2 rare,- grids 3, 4, 5, 6 and 1, and an wodeon-platei;

The respective grids 3 to l have corresponding pairs of side rods 9 liar-1.2.1.3 14, .lS- -JB, l|--l8; the anode or plate. 8 is provided with suit able supports (not shown). may be mounted on a {common header or stem is: sealed i acuum-tight into the envelope All the electrodes preach trajectories.

- editable ,positiye potential;

4. ferent from 90 degrees. Consequently, the majority of these electrons will be reflected from grid 5 over different trajectories from their ap- Therefore, by suitable spacing. of grids 4 and 5, these reflected or repelled electrons can be directed towards a region which-is outside the boundary of grid 4. Two typical reflected electron trajectories are shown in Fig. 1. In order to prevent these electrons eventually reachingthe control grid 3, a bafile platacollector. plate or shield :9 can be mounted adjacent one 'end'of grid i and connected to a If desired, the baffle ail-29 hamheattached to the side rod 'H of grid 4 .Inorderthat the grid 5 may surround the cathode 2 and besymmetrical over its effective area, the grid laterals maybe wound to a some- I, it being understood that suitable lead-inwires V V eonnecttothe respective electrodes in the-wellknown manner- When the tube of queneyeconverteror' mixer tubei the electrodes 2, 3 and 4 are connected as shown for example inrFigr-fi to'iunction-as aglocal feed-back es- Fig l is to beusedas a fire-- cillator, whereingrid '3 acts as theoscillator .con;- 7

trek and the anodergrid 4 acts. as .the oscillator plate electrode. The grid. 5,-ac'ts as the second control or modulating ;g1id,;While a grid 6 acts as a shield grid, and grid 1 acts as a :sup- .pressor'grid. In the :well-eknown mannenhthe electrons from the actual cathode z i which emerge through the openings oi gricl 4 fallin a retarding field and may form a potential minimum-even sometimes a virtual cathodebetween grids and: 5. 0n the one hand some of these electrons willtravel between the grid laterals-oi-grid 5-andthence between the grid later-- a ls oi grids- 6 and --l to the plate 58, the number of electrons reaching plate B-"being controlled hy-xthersignal' potentials appliedto gridt; On

the-other .handand provided grid :5 is not cf ieetiyely 1 negative,. some- :of. the electrons which emerge through grid-4 will .strikelthe laterals what cardioidal shape wherein the effective control portions 2% and 2t are each in the configuration substantially of a logarithmic spiral arc.

IL'iqUl'dEI'th3t the side rods l3, M, may besymmetrical -en--eaeh side of the cathode, the left hand portion 22 of the grid laterals can be formed toranysuitable*shapeto meet, and'to be fastened to, the side rod i3. Likewise, the right-hand sections can be for-medso'as to be attachable to the side rod M. V

-2 "shows an arrangement similar to :that %Fig. l butwith aslightly different configuration of grid 5. Thejparts of Fig. 2 which are functionally "the same as those of Fig. 1 bear the .7 eal e designation numerals, In Fig. 2 the effechf grid}. fionaersely-when the potential iofygrid i5, swings towards the negative direction; it also causes 1a eextaini of approachingyeleoto-chansetheir traiefliories. With the ns-- ua ovalror circular constrnctionoi grid 5;, a oon- I number of -these electrons which "ap Dina-ch the grid -,-lat eral-soigr-id Swillebe inflected or; repelled back one-r practically the sameztra- .as their trajectories of; "approach. {19th sequently, a percentage of these electrons may retnmxthrough the openin s of grid land; reach the control; g-ridfil. results in undesirable electronic hack-coupling between the control grids .3; and. 5. phenomenon is accentuated if the frequency :of the signals. applied to grid 5 are. so high that'their periodicity is comparativelylowin relation. to the transit time or theelectrons retnmingrrom grid-5-- in order to reduce toasmall percentage the number ofthesc reflected or repelled electrons from arriyi-ngat grid tive'cont-rol portionszfl .and ZLof grid 5' are each respectively in the configuration of arcs'of lo arithmie spirals, whereas the portion 124 may be substantially a circular are. 7 r

The constructions shown in Figs. 1 and 2 proride an arrangement wherein all the grid side rods can-be mounted in the same plane but the windings of grid "5 are unsymmetrical with relation to the surrounding circular electrodes 5, ,7 and 8. "Fig; 3 shows a construction wherein the grid windings 'of' grid ,5 are symmetrical both with respect 1to cathode 2 and to the remaining electrodes." .InJthi-sembodiment, the grid sec-.

tiens 2d and M are curved :to the shapeof arcs or logarithmic spirals, while the. sections'25 and 26 are :of'difterent shape. The sections 25 and 26 may-false be of logarithmic spiral arc configuratiorrhavin-g a curvature so that the points 27,

,28, are 'syminetrical with, respect to cathode-2.

. In-general, the grid'i (Fig. 3) is somewhat in 3,. the gridt5. accordingto the invention is curved V so-that'its efiectiue control. area that'is traversed by the-electronstreams from cathode 2,, is in the 1 configuration or an are off a logarithmic spiral.

I-Withsucha configuration oi; grid :ithe electrons are radiallgemitted. from cathode .2- .all annmqhthelateralsotsrid ate substantially which .howeveris manur en the configuration of an irregular oval but with the .e-fiectivecontrolportions 2B, 21, having the curvature'substantiall-y of a logarithmic spiral are. "In this embodiment the grid side rods I3 and 'M are locatedin a plane'whichis roughly 45-degl-nes with respect to the-plane of the remaining'gridside rods. i V,

addition to reducing the number of electrons which tenctitobe reflected from grid 5 to grid 3, the logarithmic spiral arc grid has, theimportant added advantage'of providing a more uniform plate-current cutofi characteristic for the control grid In many cases it is highly desirable to make sure that the effective potential around the periphery of grid 5 be substantially uniform, at leastat one; value of the grid-5-potential suchfor examples, the plate current cutoli: potential.

One manner of achieving this result is shown in Fig. 4', wherein the; parts which are similar to stantially the same configurationas'grid 5, .so

gamma 5 that itis substantially equidistant'froin grid eat least along the corresponding 5 effective control areas '20 and 2|. If the elements 2, 3 and tareof sufiicien'tly small peripheral size as compared with grid 5, the equl-distancing of grids 5 and 6 results in a close approximation of uniform effective potential on the cathode side of grid 5. 'In orderto increase further this uniformity, one or more of the remaining electrodes 6, 1(8, canfbe equally spaced from 5." In'any event, by wellknown theory, and by appropriate shaping and 'spacingof'grid 6 with respect to grid 5 the effec *tive potential'of grid 6 can be made to-insure a substantially uniform equivalent potential along the periphery of grid 5. Thus, as'shown in Fig. 5, the grid 6 is unequallyspaced from grid 5 and this spacing is designed so'that the potentials of gri'd'fi' and grid5 result in the desired uniform equivalent potential along grid 5. 'In general, the grid 6 will approximate a logarithmic spiral arc in the effective regionsZll,2|,although the origins ofthe spiral arc curvature of sections 2! 2!, of grid 6, may be displaced laterally with respect to the origins of the spiral arc curvaturesof th'ecorresponding sections of grid 5.

-' This uniform equivalent potential characteristic of the logarithmic arc spiral grid is not limited to a frequency converter or mixer tube; For example, there is shown schematically in Fig, 7, atube of the pentode type wherein the cathode 29, shield grid 30, suppressor grid 3| and anode 32 may be of conventional design; However, the control grid 33 has. its efiectivecontrol area in the form of one'or more arcs of a logarithmic spiral; Fig. 7 is of, course structurally schematic and theelectrodes :30, 3!,32 and'33, may surround the cathode 29 as shown in any of the embodiments of Figs.'1'to'5.

While the greatest advantages are achieved when the control grid of Figs. 1 to 7 is in the actual form of a logarithmic spiral arc the curvature of which is defined by thev equation =Ae tan' s where r? is the distance from the center of the spiral, coincidentwith the center of the cathode, and isthe angle of incidence of the approaching .electrons on the .gridlaterals, that is, the angle between their trajectories andthe normal to the lateral.wires. It will be understood, of course, that this curvature need not be precisely in accofdafic'dwith the above formula providing that theangle of incidence is substantially uniform for the greateizpart of the radially emitted electrons. It is within'tlie'purview of the present inventiontherefore' to provide a grid which has a substantially cardioidal configuration or any similar configuration, so that the radial electron trajectories from the cathode :in-

ter'cept or, approachithe grid laterals at asubstantially uniform angle.

. Fig; i3 represents a further modification wherein the invention is-,,8@bp@e d, 111,3; triode. The evacuated enclosing envelo'p'e"313encloses an output anode 35, a control grid 36 having a configu-- ration in plan view in the form-of a logarithmic spiral of two 360 turns, and with an elongated emitting cathode 3! wound in cross-section and at the center or origin of the logarithmic spiral. The grid turns can be supported on side rods 38, 39, 40 and 4|.

The invention is not limited to a grid structure wherein the grid is formed of a fine wire helically wound around one or more grid side rods. Thus as shown in Fig. 9, the grid 42 which may be used in place of the grid of Figs. 1-.to 5, may consist of a series of vertically parallel grid wires 63 to the cathode which are strung or supported between two end rings 44, 45, forming in eifect a squirrel cage grid. Anadditional advantage of this typeoi-grid is that the grid wires 43 can be arranged with different spacings, and these different spacings may be designed to provide the desired equivalent potential around the grid. This construction will therefore minimize the required adjustment in spacing between the grid 5 and the next succeedinggrid 6. As shown in Fig. 9, the wires 63 which are furthest removed from the cathode 2 are closer spaced than are the wires which are closer In other words, the space between the wires 43 decreases as the grid periphery recedes from the cathode 2. It will be clear that instead of using wires of different spacing to achieve the equivalent uniform potential along the grid, the wires may be of different thicknesses with their thicknesses respectively increasing as their location recedes from the cathode 2.

This same principle may be applied to the helically wound form of grid such as the grid 5 of Figs. 1 to 5 by making the grid laterals of gradually increasing thickness as they recede away from the cathode. For example, the grid laterals may be flattened out as indicated diagrammatically in Fig. 12 to provide a gradu ally decreasing interwire space with the minimum interwire spacing corresponding to the maximum remoteness of the grid laterals from the cathode 2. This manner of correcting or achieving the uniformity of potential along the grid can be applied "not only to the grid 5 but also to the grid 6 (Figs. 1 to 5).

Various changes and modifications may be made in the disclosed embodiments without departin from the spirit and scope of the invention. Thus, while a frequency converter tube is shown of the kind wherein the modulator section is a tetrode, i e., with three grids between the oscillator section and the output anode, a greater or less number of grids may be employed between the oscillator section and output anode, such for example as are employed in octode or hexode frequency converter tubes.

.Vhat is claimed is:

1. Anelectron-discharge device, comprising an electron-emitting cathode, an anode, and a grid electron-emitting cathode, an. anode, and a grid located between the cathode and anode, said grid having its eifective control eriphery-curved sub stantially in the shape of a logarithmic spiral curve. Y

3. An electron discharge device, comprising, an electron source, an anode, a control grid between said source and anode, said grid having the major partof its control'periphery curved and with one end? ofthe'curve "closer to said source than the opposite end, the curvature of said part of the grid making a substantially uniform angle with radial electron trajectories from said source which angle is different from degrees.

4. An electron-discharge device, comprising an electron source, an anode, a pair of grids between said source and anode, the grid nearer the anode having its effective control periphery in the configuration of a logarithmic spiral curve whereby the greater part of the electrons reflected thereform angle with radial electron trajectories from V said source which angl is different from 90, and another grid in spaced relation to said control grid for rendering the eli'ective potential substantially uniform along said control grid periphery.

6. An electron-discharge device, comprising an electron-emitting cathode, an anode, a, control grid between said cathode and anode, said control grid having its effective control periphery formed to a curvature which makes a substantially con- 7 stant angle with radial electron trajectories from said source which angle is different from 90, and

another grid having its effective periphery in sub- 7 stantially equally spaced relation to said control grid on the anode side thereof.

7. An electron-discharge device, comprising. an

electron-emitting cathode, an anode,a control grid between said cathode and anode, said control grid having its effective control periphery formed to a curvature which makes a substantially uni form angle with radial electron trajectories from said source which angle is different from 90, and another grid having a configuration similar to said control gr d and mounted in spaced relation thereto for rendering the efiective potential uni,-, form along said control periphery.

8. A grid electrode for electron-discharge tubes comprising a foraminous member having subi pe era co o of said mqd atcr rid is in the configuration of a logarithmic spiral curve. I Y 7 '14, A frequency converter tube according to claim 12 in which said cathode is surrounded by the control grid of the oscillator section and by the modulator grid and output anode, said modulator grid 'having' a substantially? cardioidal periphery. n

15 ,'A frequency converter tube according to claim 12in which said modulator grid surrounds said'oscillator section and is in the form of an irregular ellipse with the effective control portions i'n'the shape of a logarithmic spiral curve.

l6. A frequency converter tube according to claim '12 in which said modulator grid surrounds the cathode and has its effective control pe-,

riphery in the form of logarithmic spiral curves, and an additional similar gridsurrounds said modulator gridyto render substantially uniform the equivalent potential along said efi'ective peripheral contour of the modulator grid.

17. A multi-grid electrontube, comprising an elongated cathode; a grid surrounding said cathode, an anode surrounding said cathode, said cathode being concentrically mounted with'respect to said grid and anode, and another grid surrounding the-first grid'and comprising 'substantially two half sections each having its major stantially its entire peripherywhich is eifective on the electrons which pass therethrough in the configuration of a logarithmicspiral curve.

9. A grid electrode for electron discha rge tubes comprising'a foraminous member having a peripheral contour which is substantially cardioidal;

12. A frequency converter tube, comprising an oscillator section including an electron-emitting cathode, a control grid, and an anode-grid; a modulator section including a grid, and an output anode common to both said sections; said section's being mounted so that'the electrons from said emitting cathode serially traverse both said sections to said anode; said grid of said modulator section having a substantial part of its efiective peripheral contour of a curvature which inter-' cepts radially directed electronsat a substantially uniform angle which angle is different from 90.

13. A frequency converter tube according to claim 12 in which a substantial part of the eficcportion in the configuration. of a logarithmic spiral'cu'rve."

p 18. A frequency'converter tube, comprising an oscillator section comprising a substantially linear cathode, a control grid, and an anode-grid; 'a a modulator section comprising a second control grid and an anode which is "common to both said sections, theig'rids of saidoscillator section having side rods located in a common plane, said 'mo'du' lator grid being in the'form of an irregularellipse Number havingthe effective control peripheries thereof in the shape of logarithmic :spiral curvesjsaid modulator grid having a pair of side rods which are located on the major axis of said irregular ellipse and with the plane of said modulator grid side rodsat an angle less than degrees with respect to the plane'of the oscillator grid side rods. r

' PAUL W, CHARTON.

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